The present invention relates to the detection of stress conditions and other internal properties in structural materials, such as plastic deformation, dislocations, and other microstructure features.
The following presentation presents a brief summary of certain aspects of the state of the art, pertaining to different fields which, more often than not, have remained unrelated to each other.
Nondestructive inspection of structural materials has been used in the past and gains increasingly in importance. One uses a variety of different phenomena such as x-raying the part of probing it with ultrasonic energy. In regards to the latter, a variety of techniques have been developed including the development of transducers which launch ultrasonic waves into the structural material so that the waves may interact therewith. That interaction, for example a reflection by a flaw, fault, etc., will be detected, e.g., upon return of the wave.
One kind of these transducers is, for example, constructed in that it generates itself the ultrasonic waves which are then transmitted to and into the part under investigation. Another kind of transducer (see e.g. U.S. Pat. No. 3,850,028) is of the electromagnetic variety in that h.f. electrical energy is coupled to the part and converted therein into elastic vibrations, on the basis of the Lorentz force. Other transducers are known which use magnetostriction to convert an oscillatory magnetic field into elastic vibrations. Thus, such a transducer generates the vibration in the structural material, and the vibration propagate from the point or region of generation further into the part for interaction as described.
Aside from the foregoing, investigations by various physicists have discovered that the magnetostrictive property of steel depends on stress. See, for example, Bozorth, Ferromagnetism (D. Van Nostrand Co. Inc., Princeton) 1951, p. 656; Allen, Haborak, and Kao, "The Effect of Stress on the Magnetostriction of Iron, Nickel, and 49 Permalloy", Report THEMISUND-70-9 (Notre Dame, 1970) AD-711094; and Kuruzar and Cullity, Intern. J. Magnetism 1 (1971), pages 323-325.